Acrylic plastisols and organosols and photosensitive compositions and elements made therefrom

ABSTRACT

Thermally coalescible acrylic resin dispersions comprising particles of single-phase, surfactant-free, random acrylic polymers or copolymers, containing at least 80% by weight of acrylic units, dispersed in a surfactant-free medium that comprises a compatible liquid plasticizer that is nonvolatile at room temperature and is not a monomer of any of the polymeric components. Incorporation of a photopolymerizable, ethylenically unsaturated compound provides photosensitive dispersions useful for making relief and planographic printing plates, photoresists, and the like.

This is a division of application Ser. No. 952,467 filed Oct. 18, 1978now U.S. Pat. No. 4,309,331 which is a continuation of application Ser.No. 780,085 filed Mar. 22, 1977, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to nonaqueous acrylic resin dispersions andparticularly to acrylic resin plastisols and organosols. This inventionalso relates to acrylic resin dispersions containing photopolymerizableethylenically unsaturated compounds.

2. Description of the Prior Art

Certain polymeric resin dispersions referred to as plastisols are fluidmixtures, ranging in viscosity from pourable liquids to heavy pastes,obtained by dispersing polymeric resin particles in nonvolatile,nonaqueous liquid plasticizers, i.e., materials which are compatiblewith the polymer or resin and increase its workability and flexibilitybut are not solvents for the polymeric resin under ordinary conditionsof storage. When the plastisol has been formed into a desired shape,e.g., by molding or coating, it can be heated to coalesce the polymericresin particles and the nonvolatile liquid constituent, thereby forminga homogeneous mass. Theoretically, by appropriate choice of ingredients,any polymeric resin can be made into a plastisol. In practice, however,both the commercial use and the technical literature have focused almostexclusively on the use of polyvinyl chloride in forming plastisols, tothe extent that "plastisol" is cross-referenced to "polyvinyl chloride"in Chemical Abstracts and in many textbooks plastisols are described assuspensions of polyvinyl chloride resin. Volatile diluents can be addedto plastisol dispersions to modify their viscosity and to achievedesirable handling characteristics in coating or other formingoperations. When the dispersion contains no more than 10% volatilediluent, it is still regarded as a plastisol; when the volatile diluentcontent exceeds 10%, however, the dispersion is regarded as an"organosol", H. A. Sarvetnick, "Plastisols and Organosols", Van NostrandReinhold Company, New York (1972), page 201.

Polyvinyl chloride plastisols are known wherein the polyvinyl chlorideis copolymerized with other monomers, including acrylic monomers, thatconstitute a minority (<35% by weight) of the polymer composition. InU.S. Pat. No. 2,618,621 there are disclosed polyvinyl chlorideplastisols wherein part of the plasticizer content is replaced with anacrylic monomer, which is then conventionally thermally polymerized atthe temperature encountered in the step of coalescing the polyvinylchloride resin. French Pat. No. 73.06503 discloses plastisols preparedfrom a variety of polymers, primarily of the styrene family, with therequirements that the polymers be multiple phase and that they bedispersed in polar plasticizers.

It has now been found possible to prepare plastisols based on acrylicpolymers that are amenable to a variety of forming techniques with allof the economic, ecological, health and safety advantages attendant onsolvent-free operation. The acrylic resin compositions may be eitherplastisols or organosols, depending on the amount of volatile diluentincluded, if any.

SUMMARY OF THE INVENTION

In accordance with this invention, thermally coalescible acrylic resindispersions are prepared which comprise particles of a single-phase,surfactant-free, random acrylic polymer or copolymer, containing atleast 80% by weight of acrylic units, dispersed in a surfactant-freemedium that comprises a compatible liquid plasticizer that isnonvolatile at room temperature and is not a monomer of any of thepolymeric components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polymers suitable for use as the resin component in the dispersionsof this invention are the single-phase polymers and copolymers ofacrylic and methacrylic acids and their esters, i.e., polymers in whichonly one phase is present in the polymer particles, as evidenced by thefact that films cast from solutions of the polymers are clear. Thepolymers may be homopolymers of a given acrylic monomer or they may becopolymers made from two or more acrylic monomers. Also suitable arecopolymers made by copolymerizing one or more acrylic monomers with oneor more other ethylenically unsaturated monomers, e.g., vinyl chloride,styrene, the vinyl pyridines, and the like, so long as acrylic unitscomprise at least 80% by weight of the composition of the final polymer.Representative materials are the homopolymers and the two- andthree-component copolymers of ethyl acrylate, methyl methacrylate, andmethacrylic acid. A number of suitable combinations are illustrated inthe examples hereinafter. Particularly preferred materials are themethyl methacrylate/methacrylic acid copolymers in the ratios, byweight, of 80/20 to 99/1 and more preferably 90/10 to 98/2. The polymersmay be prepared by any of the methods familiar to polymer chemists,e.g., by emulsion, suspension, or seed polymerization. Several usefultechniques are illustrated in the examples that follow. The method ofmaking the polymer is not a part of the present invention, but will, asrecognized, have an effect on such characteristics as the inherentviscosity of the polymer and the size of the polymer particles produced.The inherent viscosity (η_(inh)) of the polymer is not a criticalfactor, but for convenient practical operation will preferably be in therange 0.1-1.5 and more preferably 0.2-1.2. When polymer viscosity ishigh, the composition will be more difficult to coalesce; when polymerviscosity is low, the form stability of the final coalesced product maybe affected adversely. Particle size, expressed as mean diameter of theparticles, is likewise not critical, but for convenient practicaloperation will preferably be in the range 0.1-20 μm and more preferably0.5-10 μm. The desirable particle size in a given instance will begoverned in part by the characteristics sought in the final product andby the forming procedures to be employed. Very small particles, e.g.,<0.1 μm, are operable, but their large available surface area tends tomake them susceptible to rapid gelation with consequent short storagelife, and to require large amounts of plasticizer that result in lowsolids/liquid ratios that are inefficient and undesirable for practicaloperations. Very large particles may limit the minimum thickness ofcoatings that can be made from dispersions containing them, and may alsorequire fusion or coalescence times that are unattractively long and/orsevere. Particle sizes in the desired range in a given instance may beobtained either directly, by choice of an appropriate polymerizationprocedure, or by grinding or milling large particles to produce smallerones, in equipment and by techniques known in the art. To improve therheology of the dispersions, it may be desirable to pretreat the polymerparticles, for example, by exposure to ammonia, as described more fullyin the examples hereinafter. The polymer particles must besurfactant-free.

To make the dispersions of this invention, the polymer particles will bedispersed in a medium that comprises a plasticizer for the polymerparticles, that is, a surfactant-free compatible liquid that isnonvolatile at room temperature and is not a solvent for the polymerunder ordinary storage conditions, but that is capable of interactingphysically with the polymer in such a way as to reduce the mutualattractive forces between polymer chains, thereby increasing theworkability and flexibility of the polymer. The plasticizer is also nota monomer of any of the polymeric components. The plasticizer can bechosen from a large number of substances known to be plasticizers forpolymers, e.g., phosphates, phthalates, sebaccates, ricinoleates,adipates, etc. Plasticizers are discussed in Sarvetnick, "Plastisols andOrganosols", Van Nostrand Reinhold Company, New York, N.Y. (1972),Chapter 3, pp. 38-59. Representative materials include: triallyl,tributyl and tricresyl phosphates; dibutyl, dicapryl, and dioctylphthalates; and others shown in the examples hereinafter. Plasticizersthat contain ether groups are operable, but generally are not preferredbecause they appear to have an adverse effect on viscosity stability andshelf life of the polymer dispersions.

The dispersing medium may also contain a volatile component, preferablyone that is a solvent or swelling agent for the acrylic polymer orcopolymer component of the dispersion. Incorporation of a volatilecomponent provides an additional means of controlling the viscosity ofthe dispersion and may frequently facilitate the forming operation,e.g., coating, and improve the rheology of the dispersion.Representative materials are methyl chloroform, chloroform, methylenechloride, and others shown in the examples. Following known practice,dispersions wherein the volatile component comprises up to 10% by weightof the total weight of the dispersion are classified as plastisols,whereas dispersions wherein the volatile component comprises more than10% by weight of the total weight of the dispersion are classified asorganosols.

The loading factor or amount of polymer solids in the liquid dispersingmedium will be governed by practical factors relating to operatingconvenience. For coatability, ease of stirring, and the like, apractical upper limit for the solids/nonvolatile liquid plasticizerratio is 60/40, and more preferred is about 50/50, for the plastisoldispersions. This consideration is less important for the organosoldispersions, where solids/nonvolatile liquid plasticizer ratios of 80/20and even 90/10 are feasible, inasmuch as any desired amount of volatilecomponent can be incorporated to give a workable viscosity and thenremoved by evaporation by heating in the course of arriving at thedesired temperature for fusing or coalescing the dispersion.

For the photosensitive dispersions and elements that are a particularlypreferred embodiment of this invention, the liquid portion of thedispersion will contain a nonvolatile photopolymerizable, ethylenicallyunsaturated compound together with any required or desiredphotoinitiator component(s), chain transfer agents, hydrogen donors,dyes and other conventional additives, all selected from the manymaterials known for their respective purposes in the photopolymer artand not forming, per se, a part of the present invention. A wide varietyof suitable materials for use as photopolymerizable monomers,photoinitiators, and the other components just mentioned is disclosed ina number of patents dealing with the photopolymer art, conveniently, forexample, in Gramas U.S. Pat. No. 3,784,378. Among the preferredphotopolymerizable monomers are a number of polyfunctional acrylic andmethacrylic monomers, such as tetraethylene glycol diacrylate anddimethacrylate, hexamethylene glycol diacrylate and dimethacrylate,polyethylene oxide diacrylate and dimethacrylate, polyethoxytrimethylolpropane triacrylate, trimethylolpropane triacrylate andtrimethacrylate, tetramethylene glycol dimethacrylate, and decamethyleneglycol dimethacrylate. Monomers that contain ether groups are operable,but ether-free monomers are preferred for viscosity stability of theplastisol. When a photopolymerizable acrylic monomer is used, it shouldnot be a monomer of any of the already-polymerized component, i.e., theacrylic polymer resin that is dispersed in the liquid component. Thus,for example, a methyl methacrylate/methacrylic acid polymer can bedispersed in a liquid that contains trimethylolpropane trimethacrylateas one component of the liquid portion. It is important that anyphotopolymerizable monomer that may be included in the dispersion shallalso contain a thermal polymerization inhibitor in an amount adequate toprevent premature polymerization of the monomer in response to the heatthat may be encountered in stirring and especially in the coalescencestep, thereby insuring that polymerization of the monomer occurs only asa consequence of photoexposure of the completed photosensitive element.The commercially available polymerization-grade monomers conventionallycontain thermal polymerization inhibitors in an amount adequate for thispurpose.

The acrylic plastisols and organosols of the invention may be formedinto articles by any of the forming procedures ordinarily used, e.g., bycoating, extrusion, molding and dipping. The forming method is notwithin the scope of the present invention. In the preferred embodimentof photosensitive elements, the dispersions of the invention may be castor extruded to form self-supporting elements, or they may be cast orcoated on transparent or nontransparent substrates to form supportedphotosensitive elements. A number of suitable substrates are disclosedin the examples hereinafter and in the aforementioned Gramas, U.S. Pat.No. 3,784,378, and are otherwise well known to those familiar with thegeneral art of photosensitive elements. The particular substrates usedand the particular structure of photosensitive elements or other objectsformed from the dispersions of the invention are not part of theinvention.

Acrylic polymers and copolymers can be dispersed in a variety ofcompatible liquid media to form fluid plastisols having solid/liquidratios of 50/50 or greater. Diluents can be added to these dispersionsto give organosols that may have substantially higher ratios of solidsto liquid, and, for both plastisols and organosols, there may beincorporated a variety of photopolymerizable monomers to permit theformation of photoimageable coatings and the like, useful for a varietyof applications, such as relief and planographic printing plates,photoresists, etc.

EXAMPLES OF THE INVENTION

The invention will be illustrated by the examples that follow, whereinparts and percentages are by weight unless otherwise noted. Data on theinherent viscosity of polymers (η_(inh)) refer to the inherentviscosities of solutions of 0.25 g polymer in 50 ml solvent, eithercloroform or 50/50 (by volume) chloroform/methanol, measured at 25° C.with a No. 50 Cannon-Fenske viscometer. Particle size values are meanparticle diameters determined by inspection of photomicrographs orelectron micrographs. Dispersion viscosities, reported in centipoises(cp.), were measured with a Brookfield RVT viscometer with a No. 5spindle. All monomers used in the examples, either to make the acrylicpolymers or to serve as photopolymerizable monomers in photosensitivecompositions, were commercially available polymerizationgrade monomerscontaining conventional amounts of polymerization inhibitors. Dyes areidentified, in some instances, by C. I. name and number as given in"Colour Index", Third Edition, The Society of Dyers and Colourists,Bradford, Yorkshire, England (1971). Performance of photosensitiveelements was measured in part by exposing them through a conventionalgraphic arts resolution guide, i.e., a series of transparent parallellines of known width in a nontransparent background, and a series oftransparent onverging lines separated by nontransparent spacing areas ofknown width, hen removing the unpolymerized composition from theunexposed areas. Performance is expressed in the examples in terms ofthe minimum width of polymerized parallel lines that could be faithfullyreproduced, and of the minimum spacing that could be obtained withoutplugging between polymerized converging lines. Filters and sieves areidentified in terms of mesh (number of openings per inch) and sieveopening (mm or μm) according to Table 21-16 on page 21-51 of Perry,"Chemical Engineers' Handbook", Fourth Edition, McGraw-Hill BookCompany, New York (1963).

EXAMPLE 1

To a solution of 0.4 g ammonium persulfate in 200 g of water was added18 ml of a solution of 1.09 g dodecyl mercaptan and 10.0 g methacrylicacid in 100 g methyl methacrylate. The suspension was stirred vigorouslyunder nitrogen and heated to 80°-85° C. At 30-minute intervals, therewas added 25 ml of the methyl methacrylate/methacrylic acid/dodecylmercaptan solution and 112 ml of a solution of 0.2 g ammonium persulfatein 450 g water. Thirty minutes after the fourth such addition, thereactor was opened to air and cooled to room temperature. The latex thathad been produced was evaporated at 55°-66° C. under nitrogen withstirring, and the residual powder was ground in a mortar, passed througha 40-mesh (˜0.38 mm) sieve, and held for 3 days in a closed containerover concentrated ammonium hydroxide. The powder was soluble at roomtemperature in chloroform and 1,1,2-trichloromethane; partly soluble,swollen and agglomerated in methylene chloride, 1,2-dichloroethane,trichloroethylene and 1,2,3-trichloropropane. It was swollen butinsoluble in methyl chloroform, perchloroethylene and carbontetrachloride. It was insoluble and not swollen in hexane.

A plastisol was prepared by mixing equal parts by weight of the powder,prepared as just described, with dibutyl phthalate. The resultant softtranslucent paste was spread at 1 mm thickness on glass and coalesced byheating for five minutes at 120° C. to give a clear, dry, soft, pliablefilm.

EXAMPLE 2

One part of polymer powder prepared as in Example 1 was mixed with 0.6part of a commercially available polyoxyethylated long chain alcohol,0.2 part of a commercially available polyoxyethylene sorbitanmonolaurate, and 0.2 part of methylene-bis-(4-cyclohexyl isocyanate).The resultant white paste was spread on glass at 1 mm thickness andheated for 5 minutes at 120° C. It coalesced to give a clear, soft filmthat swelled 12.5% by volume when immersed in 5% aqueous sodiumcarbonate. The product was suitable for use as a binder for silverhalide photographic systems. This example illustrates a crosslinkableformulation.

EXAMPLES 3-5

These examples illustrate useful upper limits for loading factor foracrylic resin plastisols, and they also show that, for a given polymerand plasticizer, relatively small changes in the solids/liquid ratio canhave a rather large effect on plastisol rheology. In addition, theseexamples illustrate a decrease in viscosity upon aging that has beenfound to be characteristic of plastisols made from methylmethacrylate/methacrylic acid (90/10) copolymers. For the dispersions ofthese examples, a polymer like that of Example 1 was mixed with dibutylphthalate by conventional high-speed sand-milling procedures. Allformulations also contained 0.2% benzotriazole and 0.07% C. I. SolventRed 109 (C. I. No. 13900/45170). Good filterability was achieved byadding a small amount of methyl chloroform, which was subsequentlyremoved by evacuation after filtration to give substantiallysolvent-free plastisols. The viscosity of the dispersion was determinedat high and low shear by varying the rotational velocity of a No. 5spindle in a Brookfield RVT viscometer, with the results shown inTable 1. Viscosities were determined for the freshly prepared plastisolsand again after aging at room temperature (1 day for Example 3; 3 daysfor Example 4). The plastisol of Example 5 was very shear-sensitive andset to a firm paste at room temperature when stirred rapidly. Theplastisols of Examples 3 and 4 were dilatant at high shear andthixotropic at low shear. They were cast and coalesced as described forpreceding examples to give clear, pliable films.

                  TABLE 1                                                         ______________________________________                                        Example                                                                               3             4             5                                         Sol./liq.                                                                             58/42         59/41         60/40                                     Visc., cps.                                                                           Initial   Aged    Initial Aged  Initial                               ______________________________________                                        at  50 rpm   6,000    2576  --      --    --                                      20 rpm   7,780    2040  16,200  2,000 --                                      10 rpm  11,600    2720  20,240  2,400 --                                       5 rpm  17,600    3760  30,240  3,440 40,000                                   1 rpm  --        --    105,000 9,600 --                                  ______________________________________                                    

EXAMPLE 6

A methyl methacrylate/methacrylic acid (90/10) copolymer (η_(inh) =0.12)was made by conventional suspension polymerization in polymethacrylicacid as the suspending agent. The resultant spherical particles wereabout 100-125 μm in diameter. The polymer was dry-milled in a ball millwith an equal volume of flint pebbles having a diameter of ˜12.5 mm forfour days. The resultant product was an impalpable powder of 2-20 μmparticle size. The powder was soluble at room temperature in methylenechloride, chloroform, 1,2-dichloroethane, trichloroethylene,1,1,2-trichloroethane and 1,2,3-trichloropropane. It was partly soluble,swollen and agglomerated in methyl chloroform, insoluble but swollen inperchloroethylene and carbon tetrachloride, and insoluble but notswollen in hexane.

An 11.1 g sample of the powder was added to a blend of 8.75 gtrimethylolpropane triacrylate, 4.00 g di-2-ethylhexyl phthalate, 1.00 g2-o-chlorophenyl-4,5-(m-methoxyphenyl)-imidazolyl dimer, 0.05 g leucocrystal violet, 0.05 g benzotriazole, 0.0125 g Michler's ketone and0.0375 g C. I. Solvent Red 109 (C. I. No. 13900/45170). This mixture wasstirred for 15 minutes at room temperature to give a fluid plastisolwith a Brookfield No. 5 viscosity of 8700 cps. It was spread on 25 μmthick polyethylene terephthalate film with a doctor knife set at 0.1 mmand heated for five minutes at 120° C. The plastisol coalesced to asmooth, clear, continuous film having a thickness of 0.05 mm whencooled.

The film was laminated at 100° C. to a copper-foil-coated phenoliccircuit board and exposed through a graphic arts resolution guide aspreviously described for one minute to radiation from a commerciallyavailable pulsed xenon source. The polyethylene terephthalate supportwas then removed, and the exposed coating was developed by extractingwith a solution of 10 g of the monobutyl ether of ethylene glycol plus 1g of borax in 90 g of water. The exposed areas had good image retention.Isolated lines having a width of 100 μm were reproduced, and there wasno line plugging at resolutions of 75-100 μm. The board could be clearlyand sharply etched with commercial ferric chloride etchant solutions,and stripped with methylene chloride.

The plastisol had good stability; viscosity was 16,000 cps. afterstanding for one day at room temperature. By contrast, a similarplastisol made with a polyether-based plasticizer, triethylene glycoldiacetate, instead of the di-2-ethylhexyl phthalate, had an initialviscosity of 13,700 cps. and this increased to >800,000 cps. after oneday at room temperature.

When the unground 100-125 μm suspension polymer was used to make asimilar plastisol, the product could not be spread to a uniform film,even at a knife clearance of 0.15 mm, and thicker coatings could not beuniformly coalesced, even after 20 minutes at 120° C.

EXAMPLE 7

A commercially available 75-125 μm suspension-polymerized poly(methylmethacrylate) homopolymer (η_(inh) =0.2) was pebble-milled as describedin Example 6 to give 2-20 μm particles, which were used to make asand-milled plastisol (solids/liquid=˜45/55) with the ingredientsdescribed in Example 6, except that the di-2-ethylhexyl phthalate wasreplaced by tricresyl phosphate/dibutyl phthalate (1/1). An equal volumeof 20-30 mesh (˜0.55-0.85 mm) sand was added to a premix of theingredients and the mixture was stirred at 0° C. for 30 minutes with adisc stirrer running at a peripheral speed of ˜300 m/min. It was thenpressure-filtered through a 200-mesh (74 μm) screen and debubbled byevacuation. The resultant plastisol had a viscosity of 6000 cps. It wasspread, coalesced, laminated and exposed as described in Example 6. Itwas developed for 15 seconds in a spray of methyl chloroform at roomtemperature. A sharp, clean image was retained. The image was etched andstripped as described in Example 6.

When a conventional, commercially available poly(methyl methacrylate)latex polymer of particle size <0.1 μm was isolated by drying at roomtemperature and comminuted by ball-milling, flowable plastisols could beprepared only at solids/liquid ratios below about 27/73. Thisdemonstrates that acrylic powders of such small particle size are notsuitable for the preparation of useful plastisols.

EXAMPLE 8

To a solution of 0.4 g ammonium persulfate in 200 g water was added 23.4ml of a solution of 4.0 g of dodecyl mercaptan in 100 g of methylmethacrylate. The suspension was blanketed with nitrogen, stirredvigorously, and heated at 80°-85° C. At 30-minute intervals, there wasadded 20 ml of the methyl methacrylate/dodecyl mercaptan mixture plus112 ml of a solution of 0.2 g ammonium persulfate in 450 g of water.Thirty minutes after the fourth addition, the reaction was terminated byadmitting air and cooling to room temperature. The product was strainedthrough nainsook fabric and held as a seed latex.

To a solution of 0.4 g of ammonium persulfate in 364 g of water wasadded 36.2 g of the seed latex described above, 32 ml of a solution of4.0 g dodecyl mercaptan, and 2.0 g of methacrylic acid in 98 g of methylmethacrylate. The suspension was blanketed with nitrogen, stirredvigorously, and heated at 80°-85° C. At 30-minute intervals, there wasadded 20 ml of the dodecyl mercaptan/methyl methacrylate/methacrylicacid solution plus 25 ml of a solution of 0.2 g of ammonium persulfatein 100 g of water. Thirty minutes after the fourth addition, thereaction was terminated and the resultant latex was strained throughglass wool and evaporated at 55°-66° C. under a stream of nitrogen withstirring.

The residue was ground in a mortar and passed through a 40-mesh (˜0.38mm) sieve to give an impalpable powder [η_(inh) =0.15 in methylenechloride/methanol (90/10)] with a glass transition temperature of 120°C. by differential scanning calorimetry. It was soluble in methylchloroform, swollen but not dissolved by carbon tetrachloride. Theresidue was used to make an organosol by the procedure of Example 7 in aformulation that comprised 11.1 g of the binder powder, 8.75 g oftrimethylolpropane triacrylate, 2.0 g tricresyl phosphate, 1.0 gbis(2-o-chlorophenyl-4,5-diphenyl) imidazole, 0.05 g leuco crystalviolet, 0.05 g benzotriazole, 0.0375 g C. I. Solvent Red 109, 0.0825 gMichler's ketone and 5 ml chloroform diluent. After sand-milling for 30minutes at 0° C., the mixture was held for 20 hours at 5° C., thenfiltered through nylon flannel at 0° C. to give a nonthixotropicdispersion that was stable at 5° C. and that could be coated, fused,laminated, exposed, developed and stripped like the product of Example7.

EXAMPLE 9

To a solution of 0.4 g ammonium persulfate in 400 g of water was added28.6 ml of a solution of 20 g methacrylic acid plus 1.07 g dodecylmercaptan in 80 g of methyl methacrylate. The suspension was stirredvigorously under nitrogen and heated at 80°-85° C. At 30-minuteintervals, there was added 20 ml of the methyl methacrylate/methacrylicacid/dodecyl mercaptan solution plus 25 ml of a solution of 0.2 gammonium persulfate in 100 ml water. Thirty minutes after the fourthsuch addition, the reaction was terminated by admitting air and coolingto room temperature. The latex was dried at 55°-66° C. under a stream ofnitrogen with stirring, and the residual powder was ground in a mortar,passed through a 40-mesh (˜0.38 mm) screen and held for 20 hours in anatmosphere of ammonia. The powder was soluble in the monobutyl ether ofethylene glycol. It was insoluble in methyl chloroform, carbontetrachloride, chloroform, methylene chloride and perchloroethylene. Itwas used to make an organosol as described in Example 8.

EXAMPLE 10

Ground methyl methacrylate/methacrylic acid (90/10) binder powderprepared as described in Example 6 was used to make a plastisol by theprocedure of Example 7, using 12.1 g of binder powder, 7.75 g oftrimethylolpropane trimethacrylate, 2.0 g tricresyl phosphate, 2.0 gdibutyl phthalate, 1.0 g bis(2-o-chlorophenyl-4,5-diphenyl) imidazole,0.05 g leuco crystal violet, 0.05 g benzotriazole, 0.0375 g C. I.Solvent Red 109, and 0.0125 g Michler's ketone. The plastisol wasfiltered through a 100-mesh (149 μm) screen and debubbled under vacuum.Viscosity was 28,400 cps. initially and 39,800 cps. after stirring forone day at room temperature. The plastisol was coated on 0.025 mm thickpolyethylene terephthalate film under a 0.1 mm thick knife at ˜1 m/min.and then passed through a 3.6 m drying oven at 105° C. The 0.05 mmproduct was clear, smooth and dry. It was used to prepare printedcircuit boards by the procedures of Examples 6 and 7.

EXAMPLES 11-23

Plastisols were made according to the procedure of Example 6 using theground methyl methacrylate/methacrylic acid (90/10) powder of Example 6in a formulation that comprised 44.4% binder powder, 35% monomer, 4%triethylene glycol diacetate, 12% tricresyl phosphate, 4%2-o-chorophenyl-4,5-(m-methoxyphenyl) imidazolyl dimer, 0.2% leucocrystal violet, 0.2% benzotriazole, and 0.15% C. I. Solvent Red 109.Viscosities and stability varied as shown in Table 2. In general, lowerinitial viscosities and better stabilities were obtained for monomersthat did not contain polyoxyethylene moieties, and for methacrylate ascompared with acrylate monomers.

                  TABLE 2                                                         ______________________________________                                        Ex-                     Viscosity, cps.                                       am-                             After After                                   ple  Monomer            Initial 4 hrs.                                                                              1 day                                   ______________________________________                                        11   Trimethylolpropane triacrylate                                                                   34,000  112,000                                                                             >800,000                                12   Trimethylolpropane  6,200   10,440                                                                               35,000                                     trimethacrylate                                                          13   Hexamethylene       3,400   27,000                                                                             Partly                                       glycol diacrylate                set up                                  14   Hexamethylene       1,800   15,550                                                                             Partly                                       glycol dimethacrylate            set up                                  15   Decamethylene      10,800   72,000                                                                             Set up                                       glycol dimethacrylate                                                    16   Trimethylene glycol                                                                              13,400  268,000                                                                             >800,000                                     dimethacrylate                                                           17   Triethylene        15,200  Set up                                                                              --                                           glycol diacrylate                                                        18   Triethylene glycol  8,800  Set up                                                                              --                                           dimethacrylate                                                           19   Polyethylene glycol                                                                              16,200  107,000                                                                             --                                           diacrylate                                                               20   Polyethylene glycol                                                                              11,700  165,200                                                                             Set up                                       dimethacrylate                                                           21   Pentaerythritol triacrylate                                                                      32,400  118,000                                                                              458,000                                22   Ethoxylated trimethylol-                                                                         23,400  Set up                                                                              --                                           propane triacrylate                                                      23   Bis(6-methacryloxy-                                                                              17,600  126,000                                                                             Set up                                       hexyl) adipate                                                           ______________________________________                                    

EXAMPLE 24

To a solution of 0.4 g ammonium persulfate in 50 g of water was added 20ml of a solution of 1.09 g dodecyl mercaptan plus 11 g methacrylic acidin 100 g methyl methacrylate. The suspension was stirred vigorouslyunder nitrogen and heated at 80°-90° C. At intervals of 10, 15, 25 and60 minutes there was added 25 ml of the dodecyl mercaptan/methacrylicacid/methyl methacrylate solution plus 112 ml of a solution of 0.20 gammonium persulfate in 450 g of water. After a further 90 minutes at88°-90° C., the latex was vacuum-filtered through fine filter paper, theresidual filter cake was twice resuspended in water and refiltered. Thefinal filter cake was air-dried and ground in a mortar to give animpalpable powder of acid number 63 and η_(inh) =0.24 in acetone. Thepowder was swollen by and partly dissolved in methylene chloride. Thepowder was used to prepare an organosol by the procedure of Example 7,using 11.1 g of the powder, 8.75 g trimethylolpropane trimethacrylate,2.0 g tricresyl phosphate, 2.0 g di-2-ethylhexyl phthalate, 1.0 gbis(2-o-chlorophenyl-4,5-diphenyl) imidazole, 0.05 g leuco crystalviolet, 0.05 g benzotriazole, 0.0375 g C. I. Solvent Red 109, 0.0125 gMichler's ketone, and 1.5 ml of methylene chloride diluent. The productwas pressure-filtered through a 100-mesh (149 μm) screen and evacuatedto give a soft, thixotropic plastisol. The plastisol was coated at athickness of 2.5 mm on polyethylene terephthalate film having athickness of 0.125 mm and heated for 5 minutes at 120° C. It coalescedto a hard, dry coating that was suitable for use as a photoimageableprinting plate.

In contrast, plastisols made from similar powders that were similarlyprepared except that as little as 7×10⁻⁵ g of sodium lauryl sulfate wasincorporated in the polymerization medium were lumpy and difficult todisperse and filter.

EXAMPLE 25

To a solution of 0.6 g ammonium persulfate in 500 g of water was added19 ml of a solution of 11 g methacrylic acid plus 1.1 g dodecylmercaptan in 100 g methyl methacrylate. The suspension was stirredvigorously under nitrogen and heated at 80°-85° C. After 12 minutes,when the initial exotherm had subsided, the remainder of the methacrylicacid/dodecyl mercaptan/methyl methacrylate solution was added dropwiseover a period of 8 hours. After further heating and stirring for 30minutes, the resultant latex was evaporated under nitrogen with stirringat 56°-65° C. The residual powder weighed 100 g and comprisedagglomerates of 0.3 μm spheres. It was comminuted in a mortar, held for24 hours at room temperature over concentrated aqueous ammoniumhydroxide and then dried for 24 hours at room temperature over sodiumhydroxide pellets. Weight gain was 1.6%, i.e., 70% of the theoreticalamount for complete conversion of all --COOH groups to -- COONH₄ groups.Predrying of the ammonia-treated powder was found to be necessary forthe preparation of plastisols with best filterability and lowestultimate viscosity. It was also found that, in general, such predryingshould be carried out for a period at least as long as was the previousNH₄ OH treatment.

The powder so prepared was used to make an organosol as described inExample 8, with the added precaution that the mixture was protected fromambient humidity by blanketing with dry nitrogen during the 0° C.milling step. This precaution served to improve filterability and reduceultimate viscosity. After pressure-filtering through nylon flannel, theorganosol had a viscosity of 200 cps. (Brookfield, No. 5 spindle, 100rpm). It was then held under oil-pump vacuum at room temperature. After20 minutes, the bubbles and diluent had been removed, and the finalvacuum was 2 mm Hg. The residual plastisol was dilatant, with BrookfieldNo. 5 viscosities of 1176 cps. at 100 rpm and 832 cps. at 50 rpm. It wasagain pressure-filtered through nylon flannel and then coated at athickness of 0.05 mm on 0.025 mm thick polyethylene terephthalate filmand coalesced by passage at 3.6 m/min. through a 3.6 m tunnel at 100° C.The resultant 0.05 mm thick coating was smooth and uniform. It could belaminated, imaged, developed, etched and stripped as described inExample 6. The plastisol was stable for many months at room temperaturewithout significant increase in viscosity, yet it could be readilycoalesced when heated to 100°-120° C.

EXAMPLE 26

A seeded latex polymerization was carried out essentially as describedin Example 8, except that the monomer mixture comprised a solution of 25g ethyl acrylate plus 10 g methacrylic acid in 65 g methyl methacrylate.The resultant latex was dried under nitrogen with stirring at roomtemperature, mortared, passed through a 40-mesh (˜0.38 mm) sieve andheld for 18 hours over concentrated aqueous ammonium hydroxide. Thepowder had a glass transition temperature of 74° C. It was used toprepare an organosol as described in Example 8. The organosol could becoated, coalesced, laminated, imaged, developed and etched as describedin Example 6.

EXAMPLE 27

A solution of 0.2 g ammonium persulfate in 100 g water was stirred undernitrogen and to it was added 29 ml of a solution of 5 g methacrylic acidplus 2 g dodecyl mercaptan in 95 g methyl methacrylate. The suspensionwas held at 80°-90° C. for 30 minutes then at 30-minute intervals therewas added 20 ml of the methacrylic acid/dodecyl mercaptan/methylmethacrylate solution plus 80 ml of a solution of 0.1 g ammoniumpersulfate in 320 ml of water. Thirty minutes after the last addition,the latex was evaporated under nitrogen with stirring at 65° C. Theresultant solid was mortared, passed through a 40-mesh (˜0.38 mm) sieve,held one day over concentrated ammonium hydroxide, then one day oversodium hydroxide pellets.

A mixture of 87.5 g trimethylolpropane trimethacrylate, 20.0 g tricresylphosphate, 10.0 g bis(2-o-chlorophenyl-4,5-diphenyl) imidazole, 0.5 gleuco crystal violet, 0.5 g benzotriazole, 0.375 g C. I. Solvent Red109, and 0.125 g Michler's ketone was stirred for about 16 hours at roomtemperature, then milled for 30 minutes at 0° C. under nitrogen with 100ml of 20-30 mesh (˜0.55-0.85 mm) sand, and pressure-filtered throughnylon flannel. An 11.9 g sample of this premix was stirred at 0° C. and11.1 g of the polymer powder was added portionwise. The resultant softpaste was held for 20 hours at room temperature. It became a flowabledispersion with a Brookfield No. 5 viscosity of 15,440 cps. at 20 rpm.An equal volume of 20-30 mesh (˜0.55-0.85 mm) sand was added, and thesuspension was milled for 30 minutes at 0° C. under nitrogen. It wasthen pressure-filtered through a 325-mesh (44 μm) screen. The filtratehad a Brookfield No. 5 viscosity of 18,200 cps. and remained uncoalescedfor many days at room temperature. It could be coated, coalesced at 120°C., imaged, developed, etched and stripped as described in Examples 6and 7.

EXAMPLE 28

To a solution of 0.2 g ammonium persulfate in 100 g water was added 29ml of a solution of 5 g methacrylic acid and 2 g dodecyl mercaptan in 95g methyl methacrylate. The suspension was blanketed with nitrogen,stirred and heated under reflux at 80°-90° C. At 30-minute intervals,there was added 20 ml of the methyl methacrylate/methacrylicacid/dodecyl mercaptan solution plus 80 ml of a solution of 0.1 gammonium persulfate in 320 ml water. Thirty minutes after the fourthsuch addition, the reaction was terminated by opening to air and coolingto room temperature. A portion of the resultant milky latex wasevaporated to dryness. The residue comprised 99% of the theoreticalyield for complete polymerization.

A second polymerization was carried out as just described except thatthe initial charge comprised 0.2 g ammonium persulfate, 79.6 g water,and 20.4 g of the latex of the first polymerization to provide 4 g ofpolymer seed, i.e., 4% of the weight of the methylmethacrylate/methacrylic acid/dodecyl mercaptan used in the secondpolymerization.

After the second polymerization was complete, the latex was evaporatedto dryness under nitrogen with stirring in a 55° C. water bath. Theresidue weighed 104 g (98% yield). It was ground in a mortar and passedthrough a 3.2 mm mesh sieve. A 33.5 g portion was loaded into a columnand anhydrous ammonia gas was passed slowly through the bed of powderfor 30 minutes.

A solution of 48 g tricresyl phosphate, 16.0 g benzophenone, 0.8 gMichler's ketone, 0.8 g bis(2-o-chlorophenyl-4,5-diphenyl)imidazole, 0.8g benzotriazole, 0.4 g tris(4-diethylamino-o-tolyl)methane, 0.2 g leucocrystal violet, and 0.28 g C. I. Basic Blue 7 (C. I. No. 42595) in 120 gtrimethylolpropane triacrylate that contained 500 ppm hydroquinone wasprepared by stirring for about 16 hours at room temperature. To 11.7 gof this solution there was added portionwise with stirring 12.5 g of theammonia-treated binder powder. The suspension was cooled in an ice bathand blanketed with nitrogen, and 20 ml of 20-30 mesh (˜0.55-0.85 mm)sand was added portionwise with disc-stirring at ˜300 m/min. peripheralspeed. After stirring for one hour, the plastisol was separated from thesand by filtration through nylon flannel and was found to have aBrookfield No. 5 viscosity of 820 cps. at 20 rpm initially, 1400 cps.after standing 24 hours at room temperature, and 2460 cps. after furtherstirring after 24 hours at room temperature. It was used to makephotoimaging circuit board resists in the manner described in precedingexamples.

Essentially similar results were obtained when the amount of seedpolymer was varied between 1% and 5% of the amount of theplastisol-forming powder. Beyond those limits, diluent-free plastisolswere much more difficult to filter.

EXAMPLE 29

A methyl methacrylate/methacrylic acid (90/10) copolymer (η_(inh) =0.12)was made by conventional suspension polymerization in water usingpoly(methacrylic acid) as the suspending agent. The resultant sphericalparticles were about 100-125 μm in diameter. The polymer was dry-milledin a ball mill with an equal volume of flint pebbles having a diameterof ˜12.5 mm for four days. The product was an impalpable powder of 2-20μm particle size. The polymer powder was soluble at room temperature inmethylene chloride, chloroform, 1,2-dichloroethane,1,1,2-trichloroethane, and trichloroethylene. It was insoluble butswollen in methyl chloroform, perchloroethylene, and carbontetrachloride. It was insoluble and not swollen in hexane.

An 11.1 g sample of the polymer powder was added to a prefilteredmixture of 1 g triethylene glycol diacetate, 3 g tricresyl phosphate,8.75 g hexamethylene glycol dimethacrylate, 1 gbis[2-o-chlorophenyl-4,5-bis(m-methoxyphenyl)]imidazole, 0.05 g leucocrystal violet, 0.05 g benzotriazole, 0.0375 g C. I. Solvent Red 109 (C.I. No. 13900/45170), and 0.0125 g Michler's ketone. When the plastisolwas held at room temperature with intermittent stirring, its viscosity(Brookfield, No. 5) was 864 cps. initially, 1652 cps. after one hour,and 42,240 cps. after one day. By comparison, a control sample of thesame composition that was held at room temperature without stirring hada viscosity of 15,550 cps. after four hours, and after one day had setup to a nonfluid gel with a 0.5-cm. thick layer of fluid plastisol onthe surface.

EXAMPLE 30

A solution of 31 g of ethyl acrylate plus 8 g of methacrylic acid in 61g of methyl methacrylate was added to a solution of 0.6 g ammoniumpersulfate in 500 g water. The suspension was blanketed with nitrogenand stirred vigorously for two hours at 80°-85° C. The resultant latexwas strained through nainsook fabric and held as "seed polymer latex".

A suspension of 30 g of the seed polymer latex in a solution of 0.6 gammonium persulfate in 400 g water was blanketed with nitrogen, stirredvigorously, and heated to 40° C. To this was added a solution of 7.75 gethyl acrylate, 2 g methacrylic acid and 0.975 g dodecyl mercaptan in15.25 g methyl methacrylate. Three more such additions were made atone-hour intervals. Thirty minutes after the final addition, the latexwas strained through nainsook fabric and held at room temperature for 10days. It was then reheated to 40° C. under nitrogen and stirred and toit was added 5 g methacrylic acid, 0.1 g sodium bisulfite, and asolution of 0.1 g ammonium persulfate in 200 g water. After one hour at40° C., the latex was evaporated under nitrogen with stirring at 25°-40°C. for two days. The residual solid was ground in a mortar, passedthrough a 40-mesh (˜0.38 mm) screen, and held for 20 hours overconcentrated aqueous ammonium hydroxide. Microscopic examinationindicated a particle size of 0.5-0.9 μm.

An 11.1 g sample of the binder powder prepared as just described wasadded to a mixture of 8.75 g trimethylolpropane trimethacrylate, 2 gtricresyl phosphate, 1 g bis(2-o-chlorophenyl-4,5-diphenyl)imidazole,0.05 g leuco crystal violet, 0.05 g benzotriazole, 0.0375 g C. I.Solvent Red 109, 0.0125 g Michler's ketone, and 7.5 ml carbontetrachloride. An equal volume of 20-30 mesh (˜0.55-0.85 mm) sand wasadded and the mixture was milled for 30 minutes at 0° C. with a discimpeller running at a peripheral speed of ˜300 m/min. The resultantorganosol remained fluid when held for one day at 5° C., but set up to afirm gel in two hours at room temperature.

EXAMPLE 31

A methyl methacrylate/methacrylic acid (93/7) copolymer powder wasprepared by procedures like those of Example 26, using 93 g methylmethacrylate, 7 g methacrylic acid and 2 g dodecyl mercaptan. The powderwas isolated from the latex by drying at 55°-66° C., ground in a mortar,held for 24 hours over concentrated aqueous ammonium hydroxide, thenheld for 24 hours over sodium hydroxide pellets.

A mixture of 29 g trimethylolpropane triacrylate, 4.3 g dioctylphthalate, 4.3 g triethylene glycol diacetate, 4.3 g tricresylphosphate, 4 g bis(2-o-chlorophenyl-4,5-diphenyl)imidazole, 0.2 gbenzotriazole, 1 g Michler's ketone, 0.3 gtris(4-diethylamino-o-tolyl)methane, 0.11 g leuco crystal violet, 0.03 gC. I. Basic Blue 7 (C. I. No. 42595) and 31.8 g methyl chloroform wasstirred for 18 hours at room temperature, then pressure-filtered throughnylon flannel.

A mixture of 19.95 g of this liquid premix, 13 g of the copolymer binderpowder already described, and 25 ml of 20-30 mesh (˜0.55-0.85 mm) sandwas milled for 30 minutes at 0° C. under nitrogen, thenpressure-filtered at 0° C. through nylon felt. The resulting organosolhas viscosities of 200 cps. initially, 292 cps. after 5 hours at 5° C.,and 824 cps. after 24 hours at 5° C. When the organosol was held at 25°C., viscosity rose as follows:

Initial: 300 cps.

After 15 min.: 344 cps.

After 30 min.: 520 cps.

After 1 hour: 1052 cps.

After 2.5 hours: 3560 cps.

After 5 hours: 86,400 cps.

After 6 hours: 380,000 cps.

I claim:
 1. A composition containing thermally coalescible acrylic resinplastisol or organosol dispersion comprising particles having a meandiameter in the range of 0.1 to 20 μm of a single-phase,surfactant-free, homopolymer, random bipolymer or tripolymer of acrylicmonomer(s) selected from the group consisting of ethylacrylate, methylmethacrylate and methacrylic acid dispersed in a surfactant-free mediumthat comprises a compatible liquid plasticizer that is nonvolatile atroom temperature and is not a monomer of any of the polymericcomponents, the weight ratio of said particles to said plasticizer beingfrom 40/60 to 90/10, and, in addition, a nonvolatile photopolymerizableethylenically unsaturated monomeric compound which is not a monomer ofany of the polymeric components and at least one photoinitiator.
 2. Adispersion according to claim 1 wherein the monomeric compound is apolyfunctional acrylic or methacrylic monomer.
 3. A dispersion accordingto claim 2 wherein the monomeric compound is trimethylolpropanetriacrylate.
 4. A dispersion according to claim 2 wherein the monomericcompound is trimethylolpropane trimethacrylate.
 5. A dispersionaccording to claim 2 wherein the monomeric compound is triethyleneglycol diacrylate.
 6. A dispersion according to claim 2 wherein themonomeric compound is triethylene glycol dimethacrylate.
 7. A dispersionaccording to claim 2 wherein the monomeric compound is polyethyleneglycol diacrylate.
 8. A dispersion according to claim 2 wherein themonomeric compound is ethoxylated trimethylolpropane triacrylate.
 9. Aphotopolymerizable element which comprises a support bearing a coalescedlayer of the composition according to claim 1.